Shortly after the launch of OS X 10.8 Mountain Lion, users of portable Macs began to report significant reductions in their battery life on Cupertino’s latest cat. Reports varied, but independent testing showed a reduction of 20 to 30 percent in battery life on 10.8 compared to the same hardware on 10.7.

According to Ars Technica, as news of the battery life problem spread, Apple reportedly began contacting users affected by the issue and asked them to log system data for Apple’s review. Mountain Lion’s first update, OS X 10.8.1, was just around the corner, but Apple made no public mention of whether the data they were collecting was being used to fix the battery life issue in the update.

In the last few days, some developers began to report improvements in their battery life while using the most recent developer build of 10.8.1. “Until I installed 10.8.1, my MacBook was showing 4h:05m after a full charge,” a developer told software aggregation site Softpedia. “After installing 10.8.1 it’s showing over 8h.”

Apple released the final build of 10.8.1 Thursday morning, although the company cited nothing about battery life in the update’s release notes. Now that we’re armed with several builds to compare, we performed battery life benchmarks on OS X 10.7.4, 10.8, 10.8.1 Build 12B17 (the prerelease developer build), and 10.8.1 Build 12B19 (the final version released to the public).

Our testbed is a 2011 15-inch MacBook Pro 2.3 GHz i7 with 8 GB of RAM and 240 GB OWC SSD. The battery has 115 cycles and is considered by the battery health monitor to be in “Normal” condition. In other words, this is not a new machine; it’s seen decent use over the past year and, we hope, its condition is representative of that of a larger percentage of Mac owners than a brand new Mac.

That’s not to say we didn’t consider a new Mac, however. For the sake of a casual comparison, we’re also testing a new Retina MacBook Pro and a 2011 13-inch MacBook Air. We’ll have the results of those tests for you in the next few days.

Our battery life test was performed by using a custom Automator application under battery-saving conditions: the screen at 50 percent brightness, keyboard illumination off, and all applications and services disabled except for WiFi. To keep the Mac running throughout the test, we disabled system and display sleep in System Preferences, and deactivated the screen saver.

Our Automator app performs the following actions:

Open TextEdit, pause 10 seconds.

Open Safari and navigate to a content-heavy website (macobserver.com), pause 20 seconds.

Navigate to a second content-heavy website (cnn.com), pause 20 seconds.

Open Mail, pause 10 seconds to allow any messages to download

Close all open applications

Log a time stamp to a text file

Repeat

We feel that these steps provide a nice balance between light and medium workflows. Most Mac users won’t be launching that many websites so frequently, but some users may engage in more battery-draining tasks like video playback or editing. It should be noted that our tests are not designed to replicate heavy workflows, such as video encoding or 3D rendering, although we are investigating a workflow that would suitably replicate those tasks for future benchmarking.

Of note, Mac Geek Gab listener “Chilled Storm,” suggested that a fix for 10.8’s battery life issues was to remove the WiFi status icon from OS X’s menu bar. We ran a separate test on 10.8 with this configuration and the results can be seen in the chart below.

So, without further ado, the numbers:

Chart by The Mac Observer

As you can see from the chart, the battery life hit caused by 10.8 Mountain Lion is significant. Our 2011 MacBook Pro lost 2 hours and 10 minutes, or 33 percent, of battery operating time following the upgrade. Removing the WiFi icon from the menu bar had no positive impact (in fact, we actually lost 5 minutes of battery life).

The prerelease build of 10.8.1 improved things a little bit, and gave us back about 30 minutes of battery life, but we were still about 100 minutes short of where we should be based on Lion’s battery numbers.

With great anticipation, we installed the final build of 10.8.1 this morning and ran our benchmark again, only to be disappointed by the results. Battery life did improve by about 17 minutes over the prerelease build, but we are still over an hour short on battery life compared to 10.7.4’s numbers, a difference of about 20 percent.

These numbers may not be final; Apple is already testing 10.8.2 with select developers, although we have no word from the company on its plans to further address battery life concerns. It’s also possible that Mountain Lion simply requires more power from the system to perform new graphical and under-the-hood tasks, and that an unfortunate result of these new features is a reduction in usable battery life.

In the end, it’s clear that 10.8.1 has brought with it a sizable increase in battery life compared to 10.8, but the initial loss caused by the upgrade to Mountain Lion was so large that MacBook battery life is still far shy of where it should be.

From here, all that portable Mac users can do is follow Apple’s Mountain Lion development and hope that they have a plan to restore battery life to 10.7 Lion-like levels in future updates. We have contacted Apple with a request for comment on the numbers we obtained but they have not responded to our inquires. We will update this article if they do.

Tune in Friday and Saturday for the results of our tests on the Retina MacBook Pro and the 2011 13-inch MacBook Air.